In a wind turbine generator system of the type of interest here, in the power flow between a rotor converting the wind energy into a rotary motion and a generator transforming the rotary motion into electric energy, a transmission with a speed increase is arranged. Since the modules of the wind turbine generator system are mostly placed within a nacelle at the top of a tower, a transmission which is as compact as possible and has the lowest possible mass is desirable. This requirement is in conflict, however, with the tendency towards ever larger wind turbine generator systems having greater power, which require more powerful transmissions, among other things. To limit their mass, the power-distributed wind turbine transmissions of interest here have been used as of late.
EP 1 240 443 A1 discloses a generic power-distributed wind turbine transmission. It is composed essentially of a symmetrically-constructed planetary transmission on the input side, consisting of at least two equally dimensioned parallel-connected power-distributed planetary stages. To combine the moment flow distributed by the planetary stages on the output side, a load-compensating differential transmission stage is connected downstream, which can be formed either as a passive type of differential or as an active type of differential in the form of a differential planetary transmission. As an alternative, the active differential can also be a differential spur-gear pair, which is axially flexibly supported and has opposing helical toothing.
In all embodiments, a normal drive shaft is provided on the input side of this power-distributed wind turbine transmission, to which either the rotor of the wind turbine generator system can be directly connected, or a distance-covering rotor shaft is connectable by means of a shaft-hub connection. On the inside of the transmission, the drive shaft is coupled to the common planet carrier of the parallel-connected planetary stages. Limiting this construction to a normal shaft as a drive shaft on the transmission input side leads to the problem, however—should the rotor be attached directly to the wind turbine transmission—that the relatively large diameter of a rotor hub must be connected to the small diameter of the drive shaft. The power flow coming from the rotor hub would have to be directed from the outside to the inside onto the drive shaft. The rotor of a wind turbine generator system does not only produce a pure torque, however. Due to its own weight forces and due to force and moment variations on the rotor blade caused by the wind and the like, the drive shaft is exposed, in particular, to disturbing bending moments and transverse forces. Apart from extreme bearing loads at the drive shaft, they can also lead to disturbances in tooth mesh in the transmission and therefore to higher wear and tear.
WO 02/14690 discloses a technical approach which tries to solve the above explained problems by arranging the rotor hub with the given large diameter directly on a planet carrier of a planetary stage on the transmission input side, dispensing with a normal drive shaft, wherein the planet carrier has been radially expanded toward the outside to a corresponding diameter. The planet carrier radially expanded beyond the diameter of the hollow gear of the planetary stage on the input side also establishes the connection to a large roller bearing, via which the rotor is supported at the fixed transmission housing or another supporting construction. This design achieves the advantage that disturbing load forces, such as bending moments and transverse forces, are directly fed to the large roller bearing via the rotor hub, and by these means into the fixed supporting structure, whereas the torque—stripped thereof—is fed from the rotor hub into the planet carrier and from there into the first planetary stage. What is driven is therefore the planet carrier, while the hollow gear is coupled with the supporting structure in a non-rotatable fashion. The output of the planetary stage is the sun gear. Due to the design chosen of the two planetary stages arranged in series, there is no power distribution within the two planetary stages, but each individual stage is dimensioned for the entire power supplied by the rotor. This is in contravention to a diameter reduction of the hollow gear and therefore indirectly of the outer diameter of the transmission, because the principle of advantageously occurring power distribution on the input side in coupled planetary transmissions is not used.
While in this technical approach, due to its construction, the disturbing bending moments and transverse forces are weakened due to feeding the power onto a large diameter, they are not, however, entirely eliminated so that the disturbing deformation of the components situated in the power flow also affects the toothing between the planetary gears and the hollow and sun gears via the planet carrier.